A girl whom you've had no physical contact with due to geographical constraints but that you date via phone, texting, email, facebook or various other social media avenues. You would adore this girl enough to send messages back and forth throughout the day and look forward to talking on the phone well beyond midnight. The couples brains would become tender lovers prior to the allowance of physical contact.

"I'm sorry, you are nice and all, but I have a braingirlfriend". "She is so far away from me now but she's always with me and my brain and I love her to death".